1. Field of the Invention
This invention relates in general to positioning or location systems and, in particular, to such a system as utilized to locate objects within an interior space or shielded environment. More specifically, but without restriction to the particular embodiments hereinafter described in accordance with the current best mode of practice, this invention relates to a location positioning system for use in a shielded environment that utilizes GPS-type signals.
2. Discussion of the Related Art
The art of proximity detection and position location has been contributed to by a number of proposed devices and systems. These include, for example, the device discussed in U.S. Pat. No. 5,311,185 to Hochstein et al. which is directed to a proximity detection device relying on a transponder that periodically transmits status signals. Transceivers are fixed at locations about a structure for receiving and transmitting signals. U.S. Pat. No. 5,363,425 to Mufti et al. incorporates an identification badge having a radio frequency (RF) transmitter. Radio frequency (RF) receivers are located in telephones in various rooms of a structure. The location of the identification tag is determined to be the room with the nearest phone. Anders et al. in U.S. Pat. No. 4,656,463, propose a passive transceiver tag which is sensed by an active transceiver. This proximity control system forms the basis for a location, identification, and measurement of movement of inventory system, commonly referred to as a LIMIS system.
Prior devices and systems, as exemplified by those discussed above, have been directed to the use of proximity detection. Typically, these devices use a radio frequency (RF) transponder and a radio frequency (RF) receiver. Proximity is measured by detection of a signal or by signal strength. Current proximity devices, therefore, lack the ability of precisely measuring the location of an object.
One current type of location position system does, however, offer the advantage of precise location. Such an existing system is known as the Global Positioning System (GPS). This system includes a number of satellites in orbit around the Earth. Each satellite produces a continuous signal which carries both a time component and a space component having a number of orbital parameters associated therewith. A GPS receiver, employed in conjunction with an appropriately programed computer, is used to receive at least four of the satellite signals and therefrom determine a precise location of the receiver. This location information is typically presented as longitude, latitude, and altitude. One critical limitation of the GPS is that it requires the satellites to be "in view" relative to the receiver. This means that no obstruction can exist between the minimum number of satellites and the receiver. The standard GPS, therefore, will not function inside a building since the GPS signal is blocked by glass, metal, foliage, soil, brick, and various other materials which cause deflection of the signal. The GPS signal is optimally employed in an environment such as a flat desert or on the high seas. Thus, while the GPS has many important uses in wide open spaces, it is not currently available for use within interior spaces or shielded environments.
In addition to the U.S. patents discussed above, other related references deal exclusively with outside signals. Such references include, for example, U.S. Pat. No. 5,051,741 to Wesby; U.S. Pat. No. 5,334,974 to Simms et al.; and U.S. Pat. No. 4,918,425 to Greenberg et al.
Positioning systems are becoming widely recognized as being more important in today's society. There is a current need in business and industry to precisely locate and/or track the movement of people and material assets such as inventory or capital equipment. Structures such as the World Trade Center or large factories, which can employ thousands of people, currently desire the ability to locate people who may require assistance in reaching their intended destination. This is also true for large theme or amusement parks and other expansive tourist areas. In addition, this current need generally applies to people, objects, and inventory whether they may be located indoors, out-of-doors, or moving therebetween. The prior art devices and systems discussed above do not meet these needs because they lack precision or are currently incapable of operating within shielded environments or interior spaces.
Thus, prior to the present invention disclosed herein below, there has not been proposed a positioning system that precisely locates an object or person by utilizing GPS or GPS-type signals in an interior space or shielded environment.